Unnikrishnan spent 14 years at the Frank Anthony Public School in Bangalore before graduating in 1995 in the ISC Science stream.[clarification needed] He wanted to join the Army, even attending school in a crew cut. His peers and teachers recalled him as being a good athlete who was active in school activities and sports events.[5] He was also a member of the school choir and enjoyed watching movies.[5][6]

He was commissioned as a lieutenant to the 7th Battalion of the Bihar Regiment[1] (Infantry) on 12 July 1999. After serving the Indian Army in different locations in Jammu and Kashmir and Rajasthan during counter insurgencies for two terms, he was selected to join the National Security Guards. On completion of training, he was assigned to the Special Action Group (SAG) of NSG on January 2007 and participated in various operations of the NSG.[8] During the 'Ghatak course' (at the Commando Wing (Infantry School), Belgaum), the most difficult course of the Army, Unnikrishnan topped the course, earning an "Instructor Grading" and commendation. He opted for the NSG commando service which he joined on deputation in 2006.[9]

During Operation Vijay in July 1999, he was regarded positively at the forward posts in the face of heavy artillery firing and small arms fire by Pakistan troops. On the evening of 31 December 1999,[clarification needed] Unnikrishnan led a team of six soldiers and managed to establish a post 200 metres from the opposing side and under direct observation and fire.[10]

On the night of 26 November 2008, several iconic buildings in South Mumbai were attacked during 26/11. One of the buildings where hostage were held was the 100-year old Taj Mahal Palace Hotel. Unnikrishnan was the team commander of 51 SAG deployed in the operation at the hotel to rescue the hostages. He entered the hotel in a group of 10 commandos and reached the sixth floor through the staircase. As the team descended the stairs, they suspected perpetrators on the third floor. A few women were held as hostages in a room which was locked from the inside. After breaking open the door, the round of fire by the perpetrators hit Commando Sunil Yadav, who was Unnikrishnan's colleague.[11]

Unnikrishan engaged the perpetrators in a firefight. He arranged for Yadav's evacuation and gave chase to those he had engaged in the firefight who, meanwhile, escaped to another floor of the hotel.[12] In the encounter that followed, he was shot from the back before later succumbing to his injuries.[13][14][15]

His last words were, "Do not come up, I will handle them," according to NSG officials.[16]

IC-58660 MAJOR SANDEEP UNNIKRISHNAN BIHAR REGIMENT/51 SPECIAL ACTION GROUP (POSTHUMOUS)

Major Sandeep Unnikrishnan led the commando operation launched on 27th November 2008 to flush out terrorists from Hotel Taj Mahal, Mumbai in which he rescued 14 hostages.
During the operation, his team came under intense hostile fire, in which one of his team members got grievously injured. Major Sandeep pinned down the terrorists with accurate fire and rescued the injured commando to safety. In the process, he was shot in his right arm. Despite his injuries, he continued to fight the terrorists till his last breath.
Major Sandeep Unnikrishnan displayed most conspicuous bravery besides camaraderie and leadership of the highest order and made the supreme sacrifice for the nation.[17]

At Unnikrishnan's funeral, mourners chanted "Sandeep Unnikrishnan Amar Rahee" (Long live Sandeep Unnikrishnan).[18] Thousands of people lined up outside his Bangalore house to pay their respects. His funeral was held with full military honours.[19][20]

Nobody represented the Kerala government (from where his ethnic roots were from) at Unnikrishnan's funeral. Local and national media criticised the decision of the politicians. However, Chief Minister of Kerala V. S. Achuthanandan and Home MinisterKodiyeri Balakrishnan called on the Unnikrishnan's family on 30 November 2008. Sandeep's father K. Unnikrishnan criticised the visit and asked them to leave. He even threatened to commit suicide if any politician from Kerala entered his home. When V.S. Achuthanandan visited his home, Unnikrishnan told Achuthanandan and his delegation that "no dog would enter my house".[21] Later, Achuthanandan controversially said that had it not been for Unnikrishnan not even a dog would have visited his parents' house.[22] Following criticism, Achuthanandan stated that he would not apologise to the family, but that he respects them.[23]